Control systems have previously been proposed for electric vehicle motors in which there are interlocks between various driver operable controls and control devices in the control system to prevent damage to the system. For example, one such interlock may be provided to prevent a control device in the form of a contactor controlling the connection of the motor for reverse and forward motoring from being operated except when the vehicle is at rest. Such an interlock, which will be referred to hereinafter as "a speed interlock", necessitates the provision of means determining whether or not the vehicle is in motion.
In the previous proposals the control system has included a speed transducer which is used both for providing logic signals for use in the speed interlock functions and for providing analog signals for the control system. The speed transducer was a mechanical device driven by the traction motor and producing a pulse train, the frequency of which was proportional to speed. Such a transducer added considerably to the cost and complication of the control system and, being a mechanical device, required maintenance.
It is an object of the invention to provide a control system for an electric vehicle traction motor incorporating at least one speed interlock function but no mechanical speed transducer.